1. Field of the Invention
The present invention relates to a method for forming a color filter for CCD cameras, various display devices (e.g., liquid-crystal display devices) and color sensors and a method for forming a colored layer or a black matrix and in particularly relates to a novel method for producing a colored layer and black matrix simply and with high resolution.
2. Discussion of the Related Art
At present, color filters are produced by various methods, e.g., (1) dyeing, (2) pigment dispersion, (3) printing, (4) ink jet, (5) electrodeposition, and (6) micelle electrolysis.
Of these, the methods (1) dyeing and (2) pigment dispersion have been highly developed technically, and widely used for producing color charge-coupled devices (CCDs). One of the major disadvantages involved in these methods is high cost resulting from a number of steps required, e.g., photolithography followed by patterning.
By contrast, the methods (3) printing and (4) ink jet, although needing no photolithography step, have their own disadvantages. For example, the method (3), hardening printed thermosetting resin dispersed with a pigment, gives the product low in resolution and uniformity of thickness. The method (4), treating a specific ink-receiving layer to make it partly hydrophilic and partly hydrophobic, and spraying an ink onto the hydrophilic portion to produce a color filter layer, gives the product low in resolution and positioning accuracy, because of high probability of causing color contamination of the adjacent filter layer.
The method (5) electrodeposition applies a high voltage of around 70 V to a patterned transparent electrode in an electrolytic solution dispersed with a pigment of water-soluble polymer, to form an electrodeposited film for coating. This procedure is repeated 3 times, to obtain a color filter of R.G.B. This method needs the transparent electrode for electrodeposition, which is patterned beforehand by photolithography, and is inapplicable to TFT liquid-crystals because of limited pattern shape. No patterning step may be necessary to effect anew, if the color filter can be monolithically formed by electrodeposition with pixel electrodes on a TFT liquid-crystal substrate. The conventional electrodeposition method, however, needs electrodeposition voltage which is too high to trigger electrodeposition by an active matrix circuit on the transparent pixel electrodes. It is therefore inapplicable to electrodeposition in which a pixel electrode of TFT is used.
The method (6) micelle electrolysis is one type of electrodeposition, which utilizes the redox reaction of ferrocene as the separating material to reduce voltage for electrodeposition, and is applicable to formation of a color filter monolithically with pixel electrodes on a TFT liquid-crystal substrate. However, a TFT to which a voltage can be applied is difficult to pass a large current, because of its high internal resistance. It is therefore difficult even for micelle electrolysis to directly form a color filter on pixel electrodes using a driving circuit for TFT. Moreover, the thin film formed by micelle electrolysis tends to be contaminated with ferrocene, surfactant or the like essential for the forming process, which separate out and are included in the film as impurities, to deteriorate its transparency. Its another disadvantage is high cost, resulting from long electrodeposition time required (several ten minutes) to decrease production efficiency, and use of a high-priced ferrocene compound as the essential electrolytic solution component. In addition, it needs an alkali metal as the prerequisite supporting salt, which may adversely affect the TFT circuit and liquid crystal, making this method inapplicable.
Japanese Patent Laid-Open No. 5-5874 (1993) discloses a method for monolithically forming a color filter on a TFT substrate, which uses a TFT-driving circuit to form a color filter layer of specific color on selected pixels by electrodeposition. This method, therefore, needs an electrodeposition apparatus and special considerations, e.g., use of separate electrodes to compensate for very high internal resistance of a TFT and secure current and voltage required for forming the film by electrodeposition. It is also necessary to protect the TFT circuit from the alkali metal present in the film, which needs to keep the solution high in conductivity for electrodeposition. This, in turn, needs a supporting salt for the solution, which is one of the causes for contamination with impurities. At the same time, a TFT of low internal resistance is needed to transmit a large current, because the conventional TFT-driving circuit is unsuitable for direct electrodeposition on pixel electrodes. The conventional electrodeposition process, involving these technical problems, is difficult to apply to production of color filters using a TFT-driving circuit. As a result, a liquid-crystal display device in which a color filter substrate and TFT substrate are monolithically formed has not been commercialized.
The photocatalytic deposition method, developed by Hoshino et. al. of Chiba University, is known as one type of micelle electrolysis in which photoreactions are used for film-making. This method is described in detail by Hoshino, Katoh, Kurasako and Komon in J. of Photography Society of Japan, vol. 59, No. 2 (1996). It uses the redox reactions of ferrocene to form a film on a section not irradiated with light, and needs an external voltage, complicating the production apparatus. It is therefore unsuitable for forming fine patterns for, e.g., color filters.
It is an object of the present invention to provide a film-making method capable of forming films by a simple process. It is another object of the present invention to provide a method for forming color filters of high numerical aperture and resolution in a well controlled manner, simply and at low cost using the above method. It is still another object of the present invention to provide an electrolytic solution for forming color filters, simple film-making apparatus which needs no electrodeposition apparatus or separate electrode for electrodeposition, and apparatus for producing a color filter.
Japanese Patent Laid-Open No. 59-90818 (1984) discloses a method for forming color filters, in which an electrode of conductive transparent thin film, divided into 2 or more regions, is formed on a transparent substrate, and electrodeposition coating is repeated by applying a voltage to a selected electrode, to coat the electrodes with different colors. It describes that the color filter is applicable to a switching device of, e.g., TFT. Japanese Patent Laid-Open No. 60-23834 discloses a method for forming a matrix type multi-color display, provided with thin-film transistor arrays formed at intersections of gate lines and source lines running perpendicularly to each other; substrate comprising display electrodes each having a color filter of its own color, and connected to drains of the thin-film transistor; and the opposite substrate with an electrical conductor over the entire surface, with a display material sandwiched by the transistor arrays and transparent conductor, characterized in that the color filters and conductive sections on the transistor arrays are used as the electrodes for electrodeposition, and colored films are selectively formed on the conductive sections by repeated electrodeposition with the solution dissolving, or dispersed with, at least an electrodepositing polymer and pigment. Japanese Patent Laid-Open No. 2-24603 discloses a method for forming a color filter, with transparent electrodes formed in a given pattern on a transparent substrate and an organic pigment layer on each transparent electrode, which is obtained by immersing the substrate and electrodes for energizing in a solution with a water-insoluble organic pigment solubilized in an aqueous micelle solution of a surfactant; and forming a given pattern of the transparent electrodes by passing electricity between the electrodes for energizing to effect the electrode-aided oxidation of the micelle on the transparent electrode to deposit the organic pigment molecules thereon, these steps being repeated at least once with an organic pigment of different spectral characteristics and another pattern of the transparent electrodes.
The present invention has been made in view of the above circumstances and provides the following film-making method, method for forming color filters, electrolytic solution, film-making apparatus, and apparatus for producing a color filter.
(1) A film-making method, wherein a film-making substrate comprising a light-transmittable substrate which supports a light-transmittable conductive thin film and a photocatalytic thin film is immersed in an electrolytic solution and irradiated with ultraviolet light directed onto the photocatalytic thin film to form a film thereon, the conductive film and the photocatalytic film being arranged on the film-making substrate in such a way that they are in contact with each other, that the conductive film is allowed to conduct to the electrolytic solution and that the photocatalytic film comes into contact with the electrolytic solution, and the electrolytic solution containing a substance which decreases in solubility or dispersibility in an aqueous liquid when its pH is changed.
The film-making method of the present invention needs neither electrodeposition apparatus nor separate electrode for electrodeposition, and hence gives a film by a simple apparatus and at a low cost. The film prepared by this method is of high quality, on a level with the one prepared by photoelectrodeposition in quality, and uniformity because no external voltage is applied during the process of making colored films.
(2) The film-making method according to (1), wherein the photocatalytic thin film is provided on the film-making substrate in such a way that the conductive thin film is partly exposed, to allow the conductive film to conduct to the electrolytic solution, when it comes into contact with the solution.
(3) The film-making method according to (1), wherein the conductive thin film is connected to an electrode on the film-making substrate, and the electrode is brought into contact with the electrolytic solution, to allow the conductive film to conduct to the electrolytic solution.
(4) A method for producing a color filter, comprising a step of irradiating a color filter producing substrate, immersed in an electrolytic solution, with ultraviolet light,
wherein said substrate comprises a light-transmittable substrate which supports a light-transmittable conductive thin film and a photocatalytic thin film in such a way that they are in contact with each other, that the conductive film is allowed to conduct to the electrolytic solution and that the photocatalytic film comes into contact with the electrolytic solution, the electrolytic solution containing a substance which decreases in solubility or dispersibility in an aqueous liquid when its pH is changed, and the ultraviolet light being directed-onto a selected region on the photocatalytic film to form a colored film thereon.
The method of the present invention for producing a color filter, using the above-described film-making method (1), can give a color filter of high numerical aperture and resolution at a low cost. Therefore, use of the color filter of the present invention allows producing a liquid-crystal display device of high accuracy at a low cost.
(5) A method for producing a color filter, comprising a step of irradiating a color filter producing substrate, immersed in an electrolytic solution, with ultraviolet light, wherein the substrate comprises a light-transmittable substrate which supports a light-transmittable conductive thin film and a photocatalytic thin film in such a way that they are in contact with each other, that the conductive film is allowed to conduct to the electrolytic solution and that the photocatalytic film comes into contact with the electrolytic solution, the electrolytic solution containing a substance which decreases in solubility or dispersibility in an aqueous liquid when its pH is changed, and the ultraviolet light being directed onto a selected region on the photocatalytic film to form a colored film thereon, the above step being repeated once or more after changing a colorant each time for the electrolytic solution.
(6) The method for producing a color filter according to (4) or (5), wherein the photocatalytic thin film is provided on the color filter producing substrate in such a way that the conductive thin film is partly exposed, to allow the conductive film to conduct to the electrolytic solution, when it comes into contact with the solution.
(7) The method for producing a color filter according to (4), wherein the conductive thin film is connected to an electrode on the color filter producing substrate, and the electrode is brought into contact with the electrolytic solution, to allow the conductive film to conduct to the electrolytic solution.
(8) The method for producing a color filter according to (4), wherein the conductive thin film and photocatalytic thin film are formed in a pattern corresponding to that of the pixels of the color filter.
(9) A method for producing thin-film transistor type color filters, comprising a step of irradiating a color filter producing substrate, immersed in an electrolytic solution, with ultraviolet light,
wherein the substrate comprises a light-transmittable substrate which supports a thin-film transistor, light-transmittable pixel electrodes, and photocatalytic thin film, arranged in such a way that the photocatalytic thin film is in contact with the electrodes while partly exposing them, and that at least the electrodes and photocatalytic film come into contact with the electrolytic solution, the electrolytic solution containing a colorant and substance which decreases in solubility or dispersibility in an aqueous liquid when its pH is changed, and the ultraviolet light being directed onto a selected region on the photocatalytic film to form a colored film thereon.
The method of the present invention for producing a TFT-assembled color filter, forming the color filter and TFT as a monolithic structure, can give a color filter of high numerical aperture and resolution at a low cost, and, at the same time, dispense with the step for aligning the color filter with the TFT, which is needed by the conventional method. Therefore, use of the color filter of the present invention allows producing a liquid-crystal display device of high accuracy at a low cost.
(10) A method for producing thin-film transistor type color filters, comprising a step of irradiating a color filter producing substrate, immersed in an electrolytic solution, with ultraviolet light, wherein the substrate comprises a light-transmittable substrate which supports a thin-film transistor, light-transmittable pixel electrodes, and photocatalytic thin film, arranged in such a way that the photocatalytic thin film is in contact with the electrodes while partly exposing them, and that at least the electrodes and photocatalytic film come into contact with the electrolytic solution, the electrolytic solution containing a colorant and substance which decreases in solubility or dispersibility in an aqueous liquid when its pH is changed, and the ultraviolet light being directed onto a selected region on the photocatalytic film to form a colored film thereon, the above step being repeated once or more after changing the colorant each time for the electrolytic solution.
(11) The method for producing a color filter according to (4), wherein the ultraviolet light is directed onto the selected region through a photomask.
(12) The method for producing a color filter according to (4), wherein an image-focusing optical system is put between a photomask and the color filter producing substrate, to form an image of ultraviolet light on the photocatalytic thin film.
(13) The method for producing a color filter according to (4), wherein the image-focusing optical lens of the image-focusing optical system and light-transmittable substrate are set 1 mm to 50 cm apart from each other.
(14) The method for producing a color filter according to (4), wherein the image-focusing optical system has a focal depth of xc2x110 to xc2x1100 xcexcm.
(15) The method for producing a color filter according to (4), wherein a mirror reflection optical system is put between a photomask and the color filter producing substrate, to form an image of ultraviolet light on the photocatalytic thin film.
(16) The method for producing a color filter according to (4), wherein the photocatalytic thin film contains titanium oxide.
(17) The method for producing a color filter according to (4), wherein the substance which decreases in solubility or dispersibility in an aqueous liquid when its pH is changed has carboxyl group in its molecule.
(18) The method for producing a color filter according to (4), wherein the substance which decreases in solubility or dispersibility in an aqueous liquid when its pH is changed is a polymer.
(19) The method for producing a color filter according to (4), wherein the polymer is a copolymer of monomers having a hydrophobic and hydrophilic group, respectively, number of the hydrophobic group accounting for 40% or more but 80% or less of the total number of the hydrophobic and hydrophilic groups.
(20) The method for producing a color filter according to (4), wherein pH level of the electrolytic solution is adjusted by a pH adjustor which has no adverse effect on the film-making characteristics.
(21) The method for producing a color filter according to (4), wherein conductivity of the electrolytic solution is adjusted by a salt which has no adverse effect on the film-making characteristics.
(22) The method for producing a color filter according to (4), wherein temperature of the electrolytic solution is controlled.
(23) The method for producing a color filter according to (4), wherein the electrolytic solution contains fine particles of a light-transmittable, conductive substance.
(24) The method for producing a color filter according to (4), wherein a black matrix is formed by photolithography which uses a black photoresist, before the colored film is formed.
(25) The method for producing a color filter according to (4), wherein after forming the colored film, a surface on which the colored film is formed coated with a black, UV-settable resin, the light-transmittable substrate is irradiated with ultraviolet light from the side opposite to the colored film, and the portion which is not set is removed, to form a black matrix.
(26) A method for producing thin-film transistor type color filters, comprising steps of
forming a color filter producing substrate provided with black matrix by coating a thin-film transistor and light-transmittable pixel electrodes, supported by a light-transmittable substrate, with a black, positive photoresist; irradiating the substrate with light from the side opposite to the thin-film transistor and light-transmittable pixel electrodes; removing the positive photoresist irradiated with light; and providing the color filter producing substrate with a photocatalytic thin film, in such a way that the photocatalytic thin film is in contact with the electrodes while partly exposing them;
immersing the color filter producing substrate in an electrolytic solution containing a colorant and substance which decreases in solubility or dispersibility in an aqueous liquid when its pH is changed, in such a way that at least the electrodes and photocatalytic film come into contact with the electrolytic solution;
irradiating the color filter producing substrate with ultraviolet light onto a selected region on said photocatalytic film to form a colored film thereon; and
repeating the above steps twice or more after changing the colorant each time for the electrolytic solution.
(27) The method for producing a color filter according to (9), wherein each of the gate and drain electrodes of the thin-film transistor is made of a low reflection material, and provided with functions similar to those of the black matrix.
(28) The method for producing a color filter according to (27), wherein each of the gate and drain electrodes is composed of two- or three-layered Cr.
(29) The method for producing a color filter according to (9), wherein a light-transmittable conductive thin film is formed on the colored film in such a way to conduct to the pixel electrodes.
(30) An electrolytic solution to be used for producing the color filter according to (4), characterized by containing a colorant and substance which decreases in solubility or dispersibility in an aqueous liquid when its pH is changed.
(31) The electrolytic solution according to (30), wherein the substance which decreases in solubility or dispersibility in an aqueous liquid when its pH is changed is a polymer having carboxyl group, and the colorant is a pigment.
(32) The electrolytic solution according to (30), wherein the polymer is a copolymer of a monomer having a hydrophobic group and a monomer having a hydrophilic group, respectively, the number of the hydrophobic groups accounting for 40% or more but 80% or less of the total number of the hydrophobic and hydrophilic groups.
(33) A film-making method, wherein a film-making substrate comprising a light-transmittable substrate which supports a light-transmittable conductive thin film and a photocatalytic thin film is immersed in an electrolytic solution, and irradiated with ultraviolet light directed onto the photocatalytic thin film to form a film thereon, the conductive film and photocatalytic thin film are arranged in such a way that they are in contact with each other, that the conductive film is allowed to conduct to the electrolytic solution and that the photocatalytic film comes into contact with the electrolytic solution, and the electrolytic solution containing a substance which can be made into film by photocatalytic reactions.
(34) A method for producing a color filter, comprising a step of irradiating a color filter producing substrate, immersed in an electrolytic solution, with ultraviolet light, wherein the substrate comprises a light-transmittable substrate which supports a light-transmittable conductive thin film and a photocatalytic thin film in such a way that they are in contact with each other, that the conductive film is allowed to conduct to the electrolytic solution and that the photocatalytic film comes into contact with the electrolytic solution, the electrolytic solution containing a colorant and a substance which can be made into film by photocatalytic reactions, and the ultraviolet light being directed onto a selected region on the photocatalytic film to form a colored film thereon.
(35) A film-making apparatus, equipped with a light source which emits ultraviolet light, image-focusing optical system having a first image-focusing optical lens and second image-focusing optical lens, photomask put between the first and second image-focusing optical lenses, and electrolysis tank containing an electrolytic solution, wherein a film-making substrate is placed in the electrolysis tank, the film-making substrate comprising a light-transmittable substrate which supports a light-transmittable conductive thin film and photocatalytic thin film in such a way that they are in contact with each other, and that the conductive film is allowed to conduct to the electrolytic solution.
The film-making apparatus of the present invention needs neither electrodeposition apparatus nor separate electrode for electrodeposition, and hence can be simply structured.
(36) The film-making apparatus according to (35), wherein the image-focusing optical system is replaced by a mirror reflection optical system.
(37) An apparatus for producing a color filter, equipped with a light source which emits ultraviolet light, image-focusing optical system having a first image-focusing optical lens and second image-focusing optical lens, photomask put between the first and second image-focusing optical lenses, and electrolysis tank containing an electrolytic solution, wherein a color filter producing substrate, comprising a light-transmittable substrate which supports a thin-film transistor, light-transmittable pixel electrodes and photocatalytic thin film, is placed in the electrolysis tank in such a way that at least the electrodes and photocatalytic film come into contact with the electrolytic solution, the photocatalytic thin film being arranged in such a way that it is in contact with the electrodes while partly exposing them.
The apparatus of the present invention for producing a color filter needs neither electrodeposition apparatus nor separate electrode for electrodeposition, and hence can be simply structured.
(38) The apparatus for producing a color filter according to (37), wherein the image-focusing optical system is replaced by a mirror reflection optical system.
(39) A color filter, comprising a light-transmittable substrate which supports a light-transmittable conductive thin film, colored film and a photocatalytic thin film, wherein the photocatalytic thin film is arranged in such a way that it is in contact with the conductive film while partly exposing it, and the colored film is formed on the photocatalytic thin film.
(40) A liquid-crystal display, at least equipped with the color filter according to (39), a substrate facing the color filter, supporting a thin-film transistor and pixel electrodes, and liquid-crystalline substance sealed between the color filter and substrate.